Steve Valley/ODA
The brown marmorated stink bug, or Halyomorpha halys, has been found near Portland and Salem.
The Oregon Department of Agriculture is asking farmers to keep an eye out for signs of it, as it's uncertain what kind of pest it could prove to be in the Pacific Northwest region.

HERMISTON, Ore. -- An Oregon State University entomologist last week found the brown marmorated stink bug on two farms in the north Willamette Valley, marking the first time the pest has been found on an Oregon farm.

At an OSU corn field day in Hermiston, Nik Wiman said he found the bug on lilacs 20 feet from wine grapes on a Sherwood farm, and on a diversified farm in Hillsboro that grows filberts, walnuts and corn.

Wiman reported the stink bug is spreading in the Willamette Valley at a "disconcerting" rate.

"We're now finding that it is pretty widespread, but the main infestation is certainly in the Portland area and the north Willamette Valley," he said.

The bug, which is disrupting pest management systems and damaging fruit crops in the Mid-Atlantic states, was first detected in the U.S. in 1996. It was first detected in Oregon in Portland in 2004.

"It is an excellent hitchhiker," Wiman said.

The bug is native to China, Japan and Taiwan, he said.

In 2010, the pest spread from East Coast urban areas to Eastern farms.

"In 2010, it started to show its true colors and moved into crops," Wiman said.

The pest is difficult to control, he said. Farmers have turned to broad spectrum insecticides, such as pyrethroids, to keep the bug in check.

Because the pest has a wide host range, numbers typically build up rapidly in nearby vegetation and re-infest fields.

Wiman said female stink bugs are more active late season as they look for food and places to lay eggs.

"They are trying to get as many calories as they can before overwintering," he said.

All stages of the bug can cause crop damage, he said, except the very early nymph stage.